Using a small volume mixer with the "continuous flow" method, the flow speed can be made very high, which accelerates the generation of turbulence in the sample flow and thus promotes efficient mixing. Dr. Denis Rousseau has developed such a mixer for resonance Raman and fluorescence spectroscopies, and we have modified the design for use with the synchrotron infrared beam. The mixer is designed such that two solutions are loaded into syringes and pumped at 2 mm/ms into a small mixing well (100 ?m wide x 100 ?m deep) etched into a stainless steel block. The mixing well is covered by a 50 ?m-thick teflon sheet, which has a 200 ?m-diameter hole aligned in the center of the mixing well. The solutions mix in the mixing well and flow through the teflon spacer into the infrared "sandwich" cell. The cell is made of two, rectangular CaF2 windows (12 mm x 25 mm), separated by a mylar Hspacer (100 ?m thick). The spacer creates a channel 200 ?m wide Hthrough the cell and provides a suitable infrared pathlength. By Hmoving the position of the infrared beam along the length of the infrared cell, different time points in the folding reaction can be probed. Since the dead time of the mixer is ~100 ?s, the time resolution of this rapid-mix flow cell is on the order of hundreds of microseconds to a few milliseconds.